I wrote the following tips to help a friend colour her comics in Photoshop. I don't know if she'll actually find them helpful but if you, like me, have a slapdash attitude to colouring comics that basically comes down to "once I've filled all the white bits, I'm done", maybe this will help.
(PC users substitute the world 'ctrl' for 'apple')
COLOURING COMICS THE SCARY GO ROUND WAY
1. Start with a 2-bit image so it is just black and white pixels, then convert to RGB or CMYK mode. You can either rub out your pencil lines or tit about with the threshold value on your scanner.
2. Select all the white areas with the magic wand (deselect 'contiguous'), then hide selection edges (View > Show > Selection edges) (it is useful to set a shortcut for this - apple-comma is usually free)
3. Fill away with the paint bucket, with 'anti-alias' deselected! I recommend only using colours out of the CMYK palette with one eye on eventually printing things.
4. Use a thin pencil tool line to join up any gaps in your linework as you go round. Deselect and reselect after you draw a black line as you will inevitably hit the black and accidentally colour the little line you just drew.
5. Keep deselecting and reselecting the white as you go, in the end you will have little isolated islands of white selected and often you can just use the square tool to plough colour over them.
6. It is fastest to learn and use keyboard shortcuts so you can go round quickly, clicking menus is annoying and they get in the way
I - eyedropper
B - brush/pencil
G - paintbucket
Apple-D - deselect all
W - magic wand (set tolerance to 3, turn anti-aliasing off)
D - default colours (black foreground, white background)
X - switch foreground and background colours
U - shape tool (set to 'fill pixels)
I hope this saves you the hundreds of hours I wasted before I reached this way of doing things! If you are conscientious about colour, you probably have your own way of doing things, but it probably takes you more than 45 minutes per page!